drop table if exists demo.tree_data;create table demo.tree_data ( id integer, code text, pid integer, sort integer);insert into demo.tree_data values(1, '中國', null, 1);insert into demo.tree_data values(2, '四川', 1, 1);insert into demo.tree_data values(3, '云南', 1, 2);insert into demo.tree_data values(4, '成都', 2, 1);insert into demo.tree_data values(5, '綿陽', 2, 2);	insert into demo.tree_data values(6, '武侯區(qū)', 4, 1);insert into demo.tree_data values(7, '昆明', 3, 1);	

-- API 如下connectby(text relname, 			-- 表名稱  text keyid_fld, 			-- id字段  text parent_keyid_fld		-- 父id字段	  [, text orderby_fld ], 	-- 排序字段  text start_with, 			-- 起始行的id值  int max_depth				-- 樹深度，0表示無限  [, text branch_delim ])	-- 路徑分隔符

-- 基本用法如下，必須通過AS子句定義返回的字段名稱和類型select * 	from connectby('demo.tree_data', 'id', 'pid', 'sort', '1', 0, '~')	as (id int, pid int, lvl int, branch text, sort int);	-- 查詢結(jié)果id | pid | lvl | branch | sort----+-----+-----+---------+------ 1 | | 0 | 1 | 1 2 | 1 | 1 | 1~2 | 2 4 | 2 | 2 | 1~2~4 | 3 6 | 4 | 3 | 1~2~4~6 | 4 5 | 2 | 2 | 1~2~5 | 5 3 | 1 | 1 | 1~3 | 6 7 | 3 | 2 | 1~3~7 | 7(7 rows)

-- 僅僅使用基本用法，只能查詢出id的相關(guān)信息，如果要查詢code等其他字段，就需要通過額外的join操作來實(shí)現(xiàn)。select 	t.id, n.code, t.pid, p.code as pcode, lvl, branchfrom (	select * from connectby('demo.tree_data', 'id', 'pid', 'sort', '1', 0, '~')		as (id int, pid int, lvl int, branch text, sort int)) as t	left join demo.tree_data as n on (t.id = n.id)	left join demo.tree_data as p on (t.pid = p.id)order by t.sort ;	 id | code | pid | pcode | lvl | branch----+--------+-----+-------+-----+--------- 1 | 中國 | | | 0 | 1 2 | 四川 | 1 | 中國 | 1 | 1~2 4 | 成都 | 2 | 四川 | 2 | 1~2~4 6 | 武侯區(qū) | 4 | 成都 | 3 | 1~2~4~6 5 | 綿陽 | 2 | 四川 | 2 | 1~2~5 3 | 云南 | 1 | 中國 | 1 | 1~3 7 | 昆明 | 3 | 云南 | 2 | 1~3~7(7 rows)

-- with recursive cte as( -- 先查詢r(jià)oot節(jié)點(diǎn)  select id, code, pid, '' as pcode, code as branch from demo.tree_data where id = 1 union all -- 通過cte遞歸查詢r(jià)oot節(jié)點(diǎn)的直接子節(jié)點(diǎn)  select origin.id, origin.code, cte.id as pid, cte.code as pcode, cte.branch || '~' || origin.code from cte join demo.tree_data as origin on origin.pid = cte.id)select id,code, pid, pcode, branch,  -- 通過計(jì)算分隔符的個(gè)數(shù)，模擬計(jì)算出樹形的深度 (length(branch)-length(replace(branch, '~', ''))) as lvlfrom cte;--  id | code | pid | pcode | branch  | lvl----+--------+-----+-------+-----------------------+----- 1 | 中國 | | | 中國   | 0 2 | 四川 | 1 | 中國 | 中國~四川  | 1 3 | 云南 | 1 | 中國 | 中國~云南  | 1 4 | 成都 | 2 | 四川 | 中國~四川~成都 | 2 5 | 綿陽 | 2 | 四川 | 中國~四川~綿陽 | 2 7 | 昆明 | 3 | 云南 | 中國~云南~昆明 | 2 6 | 武侯區(qū) | 4 | 成都 | 中國~四川~成都~武侯區(qū) | 3(7 rows)

-- step 1 執(zhí)行 select id, code, pid, '' as pcode, code as branch from demo.tree_data where id = 1 -- 結(jié)果集和working table為 id | code | pid | pcode | branch----+------+-----+-------+-------- 1 | 中國 | | | 中國

-- step 2 執(zhí)行遞歸，此時(shí)自引用cte中的數(shù)據(jù)是step 1的結(jié)果 select origin.id, origin.code, cte.id as pid, cte.code as pcode, cte.branch || '~' || origin.code from cte join demo.tree_data as origin on origin.pid = cte.id  -- 結(jié)果集和working table為 id | code | pid | pcode | branch ----+--------+-----+-------+--------------------- 2 | 四川 | 1 | 中國 | 中國~四川   3 | 云南 | 1 | 中國 | 中國~云南